Lithopone composition and process of making same



Patented July 23, 1 929. p

UNITED STATES PATENT OFFICE.

JAMES ELIOT mean, N'EwAnx, AND MARION ,L. HANAHAN, 01: EAST onANeE, NEw JERSEY, ASSIGNORS, BY MESNE ASSIGNMENTS, To THE GBASSELLI CHEMICAL COMPANY, 0E cLEvELANn, 01110, A CORIORATION or DELAWARE.

LITno oNE COMPOSITION AND PROCESS OF MAkINe SAME.

No Drawing.

This invention relates to the production of a litho one pigment having improved mixing an dispersing properties in paint vehicles, and more particularly to lithopone treat- 5 ed with a water soluble soap under conditions to allow uniform adsorption upon the surface of pigment particles.

This case is a continuation in part of our application Serial No. 742,423, filed Oct. ;8, 1924. 4

Lithoponeis a white pigment very widely used in the paint industry. It is composed of approximately 29% zinc sulfide and 71% barium sulfate. These compounds are ooprecipitated from solutions of barium sulfide and zinc sulfate, the precipitate is then dried, calcined, quenched, ground to a fine state of division, filtered, dried, and disintegrated. The use of sodium and potassium silicate has been suggested (French patent to Gadomann, 407,642 of 1909) as added agents to help make lithopone hght stable, but these materials have not roved satisfactory for i y producing a lig tsta )le product. Lithopone treated with so ium sili'cate doesnot show improved mixing and dispersion in paint vehicles. i.

The use of oil-soluble soaps in paints has also been suggested (British patent to Allendorlf, 23,687 of 1906) but they have been introduced merely to,thicken the paint and give a false body, and do not function as dispersing agents in the sense of facilitatin mixing 5 of the pigment with the vehicle. Klthough Allendorfi' states that the use ofoil-soluble soap renders the lithopone light resistant, this has proved an inoperative conception.

Very rapid progress has been made during 40 the last few years in the improvement of the lithopone process. Light resistant pigments have been developed which are also very much superior in color and hiding power as compared with the lithopone of several years ago. 5 The production of a light resistant lithopone, I however, involves one disadvantage. The ease of mixing with paint vehicles is adversely affected. The older light sensitive type of lithopone had a reputation of being rather tricky in paint formulas. It had a tendency to fight the oil. By this expression the paintman meant difficult mixing or wetting by the vehicle. This tendency is in- Applioation filed February 11,' 1928. Serial No. 253,782.

creased in the light resistant lithopone made according to the morerecent prior art.

The ordinary paint mixing operation is carried out in vertical cylimlrical iron mixers with a capacity of 50-100 gals. They are fitted with vertical rotating paddles which cut through and mix the mass of pigment and vehicle. The vehicle is introduced first, and then the proper amount of lithopone is added. Poor mixing lithopone will set up with the 7 vehicle to form a more or less plastic sticky mass. In extreme cases the mixture assumes a stiff putty-like consistency which may even break the mixer blades,'twist the driving shaft, etc. Ordinarily, however, the disad vantage lies in the extra power consumption and the greatly decreased capacity of the equipment dueto the longer mixing period required. The latter is a particularly serious disadavantage and precludes the use of poor mixing lithopone in many formulas.

An object of this invention is to overcome the poor wettmg and dispersing properties of lithopone in aint. A further object is the production 0 a coating on the pigmeht particles with aiiinity for the organic liquids'in the paint vehicle. Other objects will appear as the description proceeds.

These objects are accomplished by treatment of the lithopone in the form of a water slurry witha solution of a soap. The treatment is made in such manner that each 'pigment partlcle comes 1nto contact with the soluble Soap and has an opportunity to adsorb a protective film of the latter. The lithopone Y is treated at some point followin the calcination and prior to the final drying. This is done so that the lithopone may be in the form of a water slurry where the particles are essentially separated and free to adsorb a film of sea from the solution of the latter. Further, t e reaction of the lithopone slurry must .be neutral or alkaline-to avoid the decomposition of the soap with liberation of the insoluble fatty acids.

We have found that water soluble soaps, such as rosin soaps, and the usual water-soluble washing soaps, such as Ivory, and para soaps, the latter being the soap of sulfonated castor oil, are very effective dispersing'agents for lithopone'and produce a greatly improved light stable product. This water solubility of these soaps is highly important as it provides for adding the soap to the water slurry so that the soap will be present during the filterpressing and drying to resist any tendency of the particles to aggregate and cement to gether. y

In our preferred process we treat the lithopone slurry just prior to the final filtration and drying. This slurry contains approximately 2 parts of water to one part of pigment. It is contained in a tank equipped with finished product. In general .1% is suflicient to give a definite effect, .5% is usually suflicient for-perfect 'mixing and dispersion but greater quantities may be desirable in special cases. These percentages are for dry weight of soap based upon actual pigment content.

The following examples are given by way of illustration but it will be understood that these are not to be taken as in any way limiting our invention.

Ewample I.

Lithopone slurry containing two parts of- Water to one of pigment is introduced into a wooden tank 12 ft. in diameter and 12 ft. deep. This tank is furnished with a high speed turbine agitator, giving rapid mixing of the slurry. There are resent 12 tons of dry-lithopone and 24 tonso water. The reaction of the slurry is neutral with a pH of 7.0. In a separate smaller tub an amount of para soap corresponding to .5% based upon the lithopone, dry weight, is dissolved in water. The para soap is sulphonated castor oil neutralized with ammonium hydroxide. It contains 6Q% of total fats. The soap is dissolved in sufficient water .at 70 C. to givea 4% solution. This solution is pumped into the bottom of the lithopone slurry tank throughout a period of 6 hours. The a ita tion is continued during the addition 0 the soap and 1 hour thereafter. At the end of this period the batch is filter pressed, dried and disintegrated in the usual manner.

Example [1.

soap used in this case is the sodium salt of oleic acid. The soap solution is madeup in a separate tankfrom sodium carbonate and commerclal oleic acid known as Red oil. An

amount of oleicfacid equivalent to .1% based upon thelithopone is used. A sodium carbonate solution is first made up with an amount of soda ash equivalent to the oleic acid. This solution is heated to 60 C. and the oleic acid slowly added with efficient agitation. When saponification is completed the soap solution is pumped into the lithopone slurry in the same manner described under Example N o. I and the lithopone is finishedv as described there.

Ewample HI.

. This treatment is made in the same manner as that made under Example No. I except that 2% of a commercial washing soap is used. The soap is obtained in chip form and consists essentially of sodium stearate with some oleate. An amount of soap equal'to- 2% of the lithopone dry Weight isweighted up and dissolved at aftemperature somewhat below the boiling point. The concentration of the solu' tion is 4%. It is added to the lithopone slurry in the same manner as described under Exam ple No. I and lithopone is then finished in the same way.

In the above examples three types of soap have been cited. In addition to these we may use any other Water soluble soap including the ammonium, sodium, potassium, etc., salts of the fatty acids, of the sulfonated fats and fatty acids and of rosin. Insoluble soaps are not satisfactory presumably due to the lack of proper distribution on the lithopone particles.

The theory of the action of these soaps has already been referred to briefly. It is believed that the soap is adsorbed upon the surface of the lithopone particles to produce a more or less continuous film. w This adsorption occurs with the carboxyl end or the acid group pointed inward toward the pigment particle. This allows the hydrocarbon or non-polar end of the molecule to point outward. As a result the film around the particle is of such type that it attracts or has an aflinity for the organic liquids in the paint vehicle. This leads to easy and complete wetting of the individual particles by the paint vehicle. 7

Further, as a result of the complete wetting there is perfect dispersion of the pigment in the paint. In other words all the pigment .of paint vehicles. When the ord nary lithopone is added to mineral thinner, the wetting like mixture.

The test maybe carried out by the use of 5 grams of lithopone and addition thereto of 1.5 c. e. of mineral thinner. The mixture is then rubbed down under a spatula and a paint like product results. The ordinary lithopone of the prior art subjected to this test gives a mass which is almost dry and at least 5 c. c. of the mineral thinner are'required to break it down,even, so the mixture shows no paint like flow or brushing properties.

As many apparently widely difi'erent embodiments of this invention may be made without departing from the spirit therof, it is to be understood that we do not intend to limit ourselves to the specific embodiments thereof except as indicated in the appended claims.

We claim:

1. The process of improving the mixing and dispersing properties of lithopone pigment in paint vehicles which comprises treating the lithopone with a-water-soluble soap.

2. The process of improving the mixing and dispersing'properties of lithopone pigment in paint vehicles which comprises treating the lithopone with water-soluble soap in an amount varying from .1% to 2%.

3. The process of improving the mixing and dispersing properties of lithopone pigment in paint vehicles which comprises treatin; the lithopone with ammonium soap.

4. The process of improving the mixing and dispersing properties of lithopone pigment in paint vehicles which comprises treating the lithopone with para soap.

5. A lithopone composition of improved paint mixing properties comprising light resistant lithopone and a water-soluble soap.

6. A lithopone composition of improved )aint mixin )ro erties com )risin li ht reb b h sistant lithopone and water-soluble soap in an amount varying from .1% to 2%.

7. A lithopone composition of improved paint mixing n'opcrties comprising light resistant lithopone and ammonium soap.

8. A lithopone composition of improved paint mixing properties comprising light resistant lithopone and para soap.

9. A lithopone water-soluble soap composition capable of producing a paint like mixture when 5 grams of said composition are mixed with approximately 1.5 c. c. of a mineral thinner.

10. The process of improving the paint mixing properties of light-resistant lithopone which comprises m xing a water-soluble dispersing agent comprising a soap with the light-resistant lithopone after the calcination and quenching, and prior to drying therof,

11. 'A calcined lithopone pigment composition of improved paint-mixing properties comprising light-resistant lithopone and a water-soluble dispersing agent comprising a soap adheringto the pigment particles.

In testimony whereof we aflix our signatures.

JAMES ELIOT BOOGE. MARION L. HANAHAN. 

